1). Field of the Invention
Embodiments of this invention relate to a method and apparatus for polarizing electromagnetic radiation, particularly for use in semiconductor substrate processing.
2). Discussion of Related Art
Integrated circuits are formed on semiconductor wafers. The wafers are then sawed (or “singulated” or “diced”) into microelectronic dice, also known as semiconductor chips, with each chip carrying a respective integrated circuit. Each semiconductor chip is then mounted to a package, or carrier, substrate. Often the packages are then mounted to a motherboard, which may then be installed into a computing system.
Numerous steps may be involved in the creation of the integrated circuits, such as the formation and etching of various semiconductor, insulator, and conductive layers. Before the various layers may be etched, a layer of light-sensitive photoresist is formed on the substrate to protect the portions of the substrate that are not to be etched.
Machines referred to as photolithography steppers are used to expose the desired pattern in the photoresist layer. In order to achieve the desired pattern, light is directed through a reticle, or “mask,” and focused onto the substrate. Typically, the light sources used in the steppers emit light that is randomly polarized, which leads to a lack of precision in the exposure, as well as an increase in the size of the features that can be exposed.
Recently, attempts have been made to linearly polarize the light using a polarizing beam splitter which only captures 50 percent of the light that passes through it. However, because of the light used often has very small wavelengths, and is thus expensive to create, such a method is not cost effective as a large portion of the light is wasted.